Wildlife biologists contracted by the National Marine Fisheries Service to document spikes in dolphin mortality and to collect specimens and tissue samples for the agency were quietly ordered late last month to keep their findings confidential.

The gag order was contained in an agency letter informing outside scientists that its review of the dolphin die-off, classified as an “unusual mortality event (UME),” had been folded into a federal criminal investigation launched last summer into [last year’s BP] oil spill.

“Because of the seriousness of the legal case, no data or findings may be released, presented or discussed outside the UME investigative team without prior approval,” the letter, obtained by Reuters, stated.

A number of scientists said they have been personally rebuked by federal officials for “speaking out of turn” to the media about efforts to determine the cause of some 200 dolphin deaths this year, and about 90 others last year, in the Gulf.

Moreover, they said collected samples and specimens are being turned over to the government for analysis under a protocol that will leave independent scientists in the dark about the efficacy and outcome of any laboratory tests.